1. Field
The invention regards a collector as well as a collector arrangement for the generation of heat from incident, preferably solar radiation.
2. State of the Art
The efforts made for the use of fossil have led to a strong development of alternative energy systems. Solar energy plays a crucial part in these developments. Regarding the use of solar energy currently common, many different processes for the generation of heat for various applications have emerged besides the photovoltaic conversion of solar radiation. The most common thermotechnical process is the generation of low-temperature heat up to between 90 and 100° C. in non-concentrating solar collectors. Though non-concentrating, i.e. non-focusing collectors can produce higher temperatures up to about 150° C., the technical effort is inadequately high however. With increasing temperature level, the heat losses increase disproportionately. Through this, the degree of efficiency of these collectors becomes very low and the production of solar energy decreased drastically.
As many applications, such as e.g. in solar thermal plant technology, require much higher temperatures than those produced by non-focusing collectors, concentrating—i.e. focusing collectors have been developed in the past. Here, the solar radiation is—with the help of concentrating reflectors—led onto a focus point or a focus axis spread lengthwise along the reflectors. In doing so, the radiation is conversed into heat within an extremely small area. The surface on which the heat can be lost to the surrounding through conduction or convection is thereby reduced to a fraction of the total surface of the reflector. In a corresponding manner, the heat losses of a concentrating collectors will be reduced as opposed to a non-concentrating collector.
Concentrating collectors for the generation of heat from solar energy are very often constructed as parabolic trough collectors. The worldwide largest applications are solar farm plants where solar heat is used for the heating of a heat carrier (mostly thermal oil).
The heat carrier transfers the solar heat it receives to a steam power process. The high temperature need for this requires a high concentration of the solar radiation.
The parabolic trough collectors consist of an elongated reflector 110 with a parabolic profile in its lengthwise direction; see FIG. 8. In the focus axis of the reflector sits a absorber tube through which flows a heat carrier medium. The heat carrier medium absorbs the heat received by the tube and transports it to a heat consumer, for example a thermal power plant. Besides in such a power plant technology, parabolic trough collectors are also used to generate space heating and process heat.
The requirements to the construction of the parabolic trough collectors result from the physical principle of concentration or focusing respectively. Thus, the outline of the reflector must show high precision so that the reflected rays meet the absorber tube. If the geometry is imprecise, a considerable amount of reflected rays will not reach its goal and considerable output losses and correspondingly lower degrees of efficiency follow.
The principle of concentration requires also a precise tracking of the collectors. The collectors are then always positioned so that the reflectors are constantly aligned orthogonally to the incident solar radiation.
The parabolic trough collectors are elongated troughs. Mostly, they are serially connected in several rows into a larger collector field. Through each collector's length, additional deformations of the reflectors can be caused by torsion powers that also could lead to mis-focusing. In order to prevent this, special construction measures are chosen that avoid a torsion of the parabolic trough. Thus, some construction types use torsion tubes or intricate steel grid constructions on the back of the mirror with whose help the entire construction consisting of reflector and absorber tube is protected against deformation through torsion or wind powers.
The collector is at times exposed to strong wind. The wind powers also require an inherently stable construction of the collector, as the reflector will otherwise be deformed by the wind powers and the focus line of the absorber tube will be shifted. The parabolic trough collectors used in industrial plants and solar power plants are therefore protected against wind power deformation by intricate auxiliary constructions. These intricate auxiliary constructions for the protection of the reflectors' form stability require a high expenditures of material as opposed to the reflectors themselves and their production is—due to this high expenditure of material as well as due to the complex construction—cost intensive.
Therefore, they make the production of the entire collectors and especially the production of an entire solar energy plant disproportionally more expensive.